Olefin dimerization and codimerization catalysts comprising a tungsten salt and an aniline compound are well known in the art. Moreover, various processes for dimerization or codimerization of ethylene using these unsupported catalysts are also well known and have been successfully developed in the prior art.
One such unsupported catalyst for dimerizing ethylene to 1-butene is disclosed in U.S. Pat. No. 3,813,453 to Wideman. More specifically, the unsupported tungsten catalyst disclosed in Wideman comprises a tungsten salt such as tungsten hexachloride or tungsten hexabromide and a nitrogen containing ligand of the formula: ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are selected from the group consisting of hydrogen and alkyl radicals containing from 1 to 4 carbon atoms. Suitable nitrogen containing ligands which are within the scope of the aforementioned formula include aniline, methylaniline, butylaniline, diethylaniline, trimethylaniline and the likes thereof. The unsupported tungsten catalyst is then activated by reacting it with a suitable organoaluminum compound, such as ethylaluminum dichloride or diisopropylaluminum chloride.
U.S. Pat. No. 3,897,512 to Brown et al. discloses another unsupported tungsten catalyst composition which is useful for the dimerization or codimerization of alpha-olefins. Specifically, the catalyst composition disclosed in Brown et al. comprises a tungsten salt selected from the group consisting of tungsten hexahalides and tungsten oxyhalides; a reducing agent having one of the following formulas: R.sub.n MX.sub.3-n or R.sub.3 M.sub.2 X.sub.3 wherein n is at least 1 but not more than 2, R is an alkyl radical containing from 1 to 10 carbon atoms, X is a halide, and M is a metal selected from the group consisting of boron, aluminum, gallium and indium; and a nitrogen containing ligand of the formula NR'R"R'" wherein R', R" are selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl, alkenyl and alkaryl; R'" is selected from the group consisting of hydrogen, alkyl, and alkenyl; and R', R" and R'" may contain from 1 to 20 carbon atoms when not hydrogen; and when R', R" and R'" are hydrocarbon, the hydrogen atoms attached to the carbon atoms may be mono- or polysubstituted by at least one member of the group selected from halogen, amino, nitro, cyano, alkoxy, carboxy and carboalkoxy; and two members of R', R" and R'" may be joined by carbon-carbon bonds to form a heterocyclic saturated ring. Representative compounds which encompass the formula NR'R"R'" include ammonia, n-butylamine, cyclohexylamine, aniline, N-methylaniline, 2,4,6-trimethylaniline and the likes thereof.
Similar unsupported tungsten-based catalysts as discussed hereinabove, which comprise a tungsten salt and a nitrogen containing compound such as aniline, are also disclosed in U.S. Pat. Nos. 3,903,193 to Maly et al. and 5,059,739 to Hendriksen.
Despite the current state of the art discussed hereinabove, none of those references disclose the supported tungsten-based catalyst composition of the present invention which has a far greater thermal stability as compared to the aforementioned unsupported tungsten-based catalysts. The superior thermal stability enables the supported catalyst composition of the instant invention to be successfully employed in reaction schemes that require or prefer high temperatures, such as commercially important fixed bed dimerization reactors.